Field of the Invention
The present invention relates to a power reception apparatus, a power transmission apparatus, a non-contact power supply system, a power reception method, and a power transmission method.
Description of Related Art
As one type of short-range wireless communication, there is wireless communication by near field communication (NFC) using a frequency of 13.56 MHz as a carrier frequency. On the other hand, there is also proposed a technique of non-contact power supply by a magnetic resonance method using a coil that is used for NFC communication.
In the non-contact power supply using magnetic resonance, a power transmission side resonance circuit including a power transmission side coil is disposed in power supply equipment, a power reception side resonance circuit including a power reception side coil is disposed in electronic equipment as power receiving equipment, and resonance frequencies of the resonance circuits are set to be the same reference frequency. Then, alternating current is supplied to the power transmission side coil so as to make the power transmission side coil generate an alternating magnetic field of a reference frequency. Then, the alternating magnetic field propagates to the power reception side resonance circuit resonating at the reference frequency so that alternating current flows in the power reception side coil. In other words, power is transmitted from the power transmission side resonance circuit including the power transmission side coil to the power reception side resonance circuit including the power reception side coil.
Note that a technique related to the above description is disclosed in JP-A-2014-33504.
Typically, only the electronic equipment corresponding to the power supply equipment is placed on a power supply table (a power supply mat or a power supply cradle) of the power supply equipment so that desired power supply (power transfer) is performed. However, a foreign object that does not correspond to the power supply equipment may be placed on the power supply table by mistake. Here, the foreign object means, for example, an object (such as a card) having a wireless IC tag with an antenna coil of 13.56 MHz that does not respond to NFC communication. Otherwise, the foreign object means, for example, electronic equipment that has the NFC communication function itself, but the function is disabled by a switch. For instance, a smart phone with the NFC communication function, which is disabled by software setting can be the foreign object. In addition, a smart phone with the enabled NFC communication function but without power receiving function is classified into the foreign object.
In a state where such the foreign object is placed on the power supply table, if the power supply equipment performs power transmission operation, the foreign object may be broken down by ferromagnetic field generated by the power transmission side coil. For instance, the ferromagnetic field in the power transmission operation may cause an increase of a terminal voltage of the coil of the foreign object on the power supply table up to 100-200 V. If the foreign object is not made to withstand such a high voltage, the foreign object is broken down.
In addition, when an abnormality occurs in the electronic equipment on the power reception side during power transmission, countermeasure of power transmission stop or the like can protect the electronic equipment. In order to perform power transmission stop or the like, it may be possible to inform the power supply equipment about the occurrence of abnormality via communication. However, performing such communication requires modulation of an electromagnetic wave and is usually difficult because of legal restrictions in reality. It is desired to develop a technique that is useful for controlling power transmission by informing the power transmission side about occurrence of abnormality without modulating the electromagnetic wave when the abnormality of the power reception side occurs.